Peptide hormones (adipokinetic hormones, AKH) released from the corpora cardiaca control lipid metabolism in insects which use lipids as fuel for flight. The timing of the release of AKH during flight is not well understood. Larvae contain identical or very similar peptides, but there is no indication that these hormones regulate lipid metabolism in larvae. In larvae of Manduca sexta a peptide of this type mobilizes carbohydrates of fat body by activating glycogen phosphorylase during starvation. This peptide has been called glycogen phosphorylase activating hormone (GPAH). The peptide from larvae has been isolated and will be sequenced to determine whether GPAH is identical to AKH. The role of AKH in initiation and sustaining flight metabolism needs to be defined more exactly. To achieve this, AKH will be quantitatively determined in hemolymph and corpora cardiaca during different physiological situations and the synthesis of AKH in the intrinsic neurosecretory cells of the corpora cardiaca will be examined. Antibodies will be made to AKH and, if necessary, to GPAH and used to measure AKH (GPAH) and correlate its levels with lipid mobilization and activation of glycogen phosphorylase. Using antibodies, the cDNA and the gene coding for AKH will be isolated and will be characterized. The structure of the gene will help us to understand the synthesis of AKH.